1. Field of the Invention
This invention relates to a method and apparatus to retain rotatable cutter cones on bearing journals of earth boring rock bits.
More particularly, this invention relates to a means to retain a rotary cone on the bearing journal of a rock bit by utilizing a split toroidal ring that is deformed and "threaded" into a groove formed between the cone and the journal.
2. Description of the Prior Art
Over the years several methods have been patented to retain rotary cutters onto journals of rock bits.
U.S. Pat. No. 3,746,405 describes a three cone rock bit, one of the embodiments of which describes a combination which includes a snap ring cone retention method. To assemble the rotary cone onto the journal, the split snap ring is radially compressed within a radially disposed groove formed in the journal. The depth of the groove is sufficiently deep to completely contain the snap ring so that the cone may slip over the outer surface of the snap ring during assembly. A complementary radially disposed groove is formed in the cone, the depth of the groove being about half the thickness of the snap ring. When the complementary groove in the cone registers with the groove in the journal, the snap ring moves into the groove in the cone, thus retaining the cone onto the journal.
U.S. Pat. No. 4,157,122 describes yet another method to assemble a rotary cone onto a journal bearing of a rock bit. Complementary grooves are formed in a journal bearing sleeve and the rotary cone. The sleeve is retained on a cone spindle bearing by an annular flange at the end of the spindle. The cone is axially moved over the journal bearing sleeve to align the two radially disposed grooves in the journal bearing sleeve and the cone. A hole is drilled through the exterior of the rotary cone in alignment with the radially disposed groove adjacent the cone bearing surface. The hole formed in the cone tangents the annular groove in the cone such that a retention rod, when placed in the hole, moves into the registering grooves or slots formed between the journal sleeve and the cone. The rod is forced into the registering grooves to retain the rotary cone onto the journal bearing sleeve. The spindle bearing, with assembled cone rotatably attached, is then welded into a recess in a leg of the rock bit.
U.S. Pat. No. 4,161,343 teaches still another cone retention system. The method taught incorporates one or more radially disposed rods in the journal bearing that engage with an annular groove formed in a rotary cone. When the groove in the cone aligns with the radially disposed holes in the journal, the rods are moved radially outwardly by a pointed pin that engages the inward ends of the rod and urges the rods radially into engagement with the groove in the cone. The pin is subsequently welded within the bearing journal, thus forcing the rods into engagement with the groove in the cone.
Two closely related patents issued to Hughes Tool Company, U.S. Pat. Nos. 4,236,764 and 4,344,658, describe a snap ring cone retention method that functions as follows. Again, a radially disposed groove is formed in the journal and a complementary groove is formed in the cone. When the two grooves are in registering alignment, a snap ring retained or forced into the groove in the journal snaps into the groove in the cone to rotatably retain the cone onto the journal. A further refinement includes a means to prevent the cone from falling off the journal by a special radial alignment of the registering grooves in the journal and the cone. The snap ring retaining the cutter onto the journal is urged toward the annular cone retainer groove when the cone is subjected to an inward thrust, thus preventing the cone from becoming disengaged from the journal bearing. The later commonly assigned '658 patent further refines the relationship of the snap ring with the complementary grooves formed between the journal and the cone.
Finally, U.S. Pat. No. 4,444,518, assigned to the same assignee as the present invention, describes still another cone retention method that utilizes spring means in combination with segmented cone retention means to retain a rotary cone onto a journal. The apparatus taught in the '518 patent basically utilizes a series of segmented rings to retain the rotary cone onto the journal. The segmented rings, for example, are inserted into a relatively deep annular channel formed transverse to the axis of the journal of a rock bit leg assembly. A complementary channel, shallow in depth, is formed in the cone. The cone, when properly positioned on the journal, closes out the channel formed in both the cone and the journal. Upon assembly, the segments are urged within the deep groove or channel in the journal such that each of the segments do not protrude beyond the bearing surface as the cone is passed over an end of the journal. Means are provided adjacent the cone retention segments to accept a spring biasing means to urge each segment away from the bottom of the deep groove in the journal. When the cone is placed over the journal, each of the segments, when they register with the complementary groove in the journal, snaps into place; thus locking the cone onto the journal.
The present invention differs from all of the aforementioned prior art in that a toroidal split ring is utilized that is "threaded" onto a journal bearing during assembly of the rotary cone onto the journal. The cone, with the split ring contained within the cone, is placed over the end of the journal. A tangential opening for the split ring is formed in the journal such that an end of the split ring will engage the opening in the journal to guide the end of the split ring into the journal retention groove as the cone is rotated onto the journal. An angularly disposed pin connected to the cone forces an end of the split ring into engagement with the tangential opening formed in the journal to guide the split end of the ring into the cone retention annular groove in the journal. Rotation of the cone with respect to the journal forces the end of the toroidal ring into the journal retention groove. A 360.degree. rotation of the cone fully engages the toroidal split ring into the groove in the cone, thereby retaining the cone onto the journal. Once the split ring is forced into the radially disposed groove in the journal, the toroidal ring returns or "snaps back" to its original shape.
The toroidal split ring of the instant invention does not have to be compressed during assembly of the cone onto the journal. When prior art snap rings spring back after assembly, a gap exists between ring ends that could interfere with the free rotation between the relative parts, namely, the journal and the cone. There is essentially no gap between the toroidal ring ends, thereby providing a stronger and less abrasive means to retain the cone on the journal. A smooth rotational potential therefore exists between the relative parts.
Moreover, snap rings or the like require that one of the registering grooves be radially deep enough to completely contain the compressed snap ring during assembly of the cone onto the journal. This necessarily results in a weakened journal or cone due to the removal of metal from either the cone or the journal. This is especially critical with respect to the journal in that deep annular grooves in the journal provide a weakened area that could cause stress fractures through the recessed area. The present invention requires the radial depth of the registering grooves be only deep enough to accept one-half the radial cross section of the cone retention ring, thereby removing the minimum amount of metal from the journal and the cone.
Additionally, the toroidal split ring of the present invention does not radially engage either the journal or the cone when assembled. The ring freely "floats" in the annular registered grooves in the journal and the cone. The surface feet per minute "slip" velocities are therefore reduced by about half with respect to the ring, the cone and the journal bearing, thereby resulting in less wear and longer rock bit life.